Schizophrenia is a debilitating disorder afflicting 1% of the world's population. The development of effective medications to treat schizophrenia relies on advances in characterizing the underlying pathophysiology. Chlorpromazine and other phenothiazines are considered first generation antipsychotics (termed “typical antipsychotics”) useful in the treatment of schizophrenia.
Adrenoleukodystrophy, or X-linked adrenoleukodystrophy, is an inherited life-threatening metabolic rare disease. It primarily affects myelination throughout the nervous system, the adrenal cortex, and the Leydig cells in the testes where very-long chain fatty acids accumulate. The adrenoleukodystrophy patient population is heterogeneous, with clinical phenotypes that include progressive neurodegenerative decline leading to vegetative state in children (childhood cerebral X-linked adrenoleukodystrophy). Treatments for adrenoleukodystrophy are include hematopoietic stem cell transplant, which results in a high-survival rate (92% 5-year survival; Peters et al., “Cerebral X-linked adrenoleukodystrophy: the international hematopoietic cell transplantation experience from 1982 to 1999,” Blood, 104: 881-888 (2004)); however, this treatment is limited to and effective with only a small adrenoleukodystrophy subpopulation, with success typically coming when it is performed in the early stages of the disease.
Adrenoleukodystrophy patients have one or more mutations to the ABCD1 gene, which encodes the peroxisomal ATP-binding cassette transporter. Subsequently, very-long chain fatty acids build up in affected cells, leading to oxidative stress and eventually metabolic failure resulting in cell death, features common to human patients and animal models (Fourcade, S, et al. “Early oxidative damage in neurodegeneration Underlying X-adrenoleukodystrophy,” Human Molecular Genetics, 17: 1762-1773 (2008); López-Erauskin, J, et al., “Antioxidants halt axonal degeneration in a mouse model of X-adrenoleukodystrophy,” Annals of Neurology, 70: 84-92 (2011)).
Antioxidant therapy is a promising therapy for the treatment of adrenoleukodystrophy and other diseases that involve oxidative stress. At the cellular level, antioxidants have been demonstrated to normalize biomarkers of oxidative stress. N-acetylcysteine (“NAC”) is a prodrug of cysteine, which serves as the limiting reagent in the synthesis of glutathione, the body's major antioxidant. When given as an adjuvant therapy to hematopoietic stem cell transplant in advanced stage childhood cerebral X-linked adrenoleukodystrophy patients, patient survival outcome greatly improves with NAC treatment (Miller, W, et al., “Outcomes after allogeneic hematopoietic cell transplantation for childhood cerebral adrenoleukodystrophy: the largest single-institution cohort report,” Blood, 118: 1971-1978 (2011); Tolar, J, et al., “N-acetyl-L-cysteine improves outcome of advanced cerebral adrenoleukodystrophy.” Bone Marrow Transplant, 39: 211-215 (2007)). However, brain penetrance is low and the long-term risks and benefits remain unknown.
Inherited mitochondrial diseases (e.g. Leigh syndrome, Alpers′ disease, and MELAS) affecting the CNS are highly variable, and often result in the progressive loss, or dysfunction, of neurons or neuroglial cells. In many cases, the pathogenesis is a result of disruption of mitochondrial respiratory chain processes, which can then increase the generation of reactive oxidative species (ROS), due to mutations in mitochondrial or nuclear DNA. Antioxidant therapy, specifically N-acetylcysteine, acts to decrease ROS and increases glutathione levels, which concomitantly increase cell survival and function.
A range of other diseases share common pathophysiology with abnormal glutamate signaling and heightened levels of oxidative stress, particularly with System xc-, a glutamate-cystine antiporter. Therefore, by engaging a single target, e.g. System xc-, which is at the junction of two distinct metabolic pathways, NAC, NAC derivatives and related molecules, may effectively treat these wide-ranging, and seemingly unrelated, diseases and disorders. This has been partially demonstrated in clinical study with NAC treatment of trichotillomania (Grant, J E, et al., “N-Acetylcysteine, a Glutamate Modulator, in the Treatment of Trichotillomania,” Arch Gen Psychiatry, 66: 756-763 (2009)). System xc-, NAC, and disturbances in glutamate signaling and oxidative stress are also linked to other diseases that include, but are not limited to, Huntington's disease (Frederick, N M, et al., “Dysregulation of system xc(-) expression induced by mutant huntingtin in a striatal neuronal cell line and in R6/2 mice,” Neurochem. Int., 2014; 76: 59-69), hypoxic-ischemic encephalopathy (Wang, X, et al., “N-acetylcysteine reduces lipopolysaccharide-sensitized hypoxic-ischemic brain injury,” Ann. Neurol., 61: 263-271 (2007)), HIV-associated neurocognitive disorder (Vázquez-Santiago, F J, et al., “Glutamate metabolism and HIV-associated neurocognitive disorders,” J. Neurovirol., 20: 315-331 (2014)).
Schizophrenia may be associated with abnormal glutamate signaling and diminished glutathione levels. Impaired cystine-glutamate antiporter activity can lead to increased oxidative stress and depleted glutathione, as well as abnormal glutamate neurotransmission, synaptic connection, and gene expression, all of which are observed in schizophrenia. In addition, impaired cystine-glutamate antiporter activity and faulty glutamate neurotransmission bear on the issue of uncontrolled drug use, i.e., drug addiction.
Cysteine prodrugs, such as NAC, drive cystine-glutamate exchange by apparently elevating extracellular cystine levels, thereby creating a steep cystine concentration gradient.
However, alternatives to NAC are needed. NAC undergoes extensive first pass metabolism requiring the usage of high doses that limit the utility of the drug and, potentially, increase the chances of side effects due to the buildup of metabolized by-products. The compounds of the present invention are designed to substantially avoid the problem of first pass metabolism and therefore exhibit increased efficacy as compared to NAC and other prior cysteine prodrugs. In addition, NAC demonstrates poor CNS penetration due to an inability to cross the blood brain barrier.
Accordingly, there is a need for novel compounds that would have a reduced incidence of problems associated with NAC. The compounds of the present invention are designed to substantially avoid the problems of first pass metabolism and poor CNS bioavailability, thereby exhibiting increased efficacy as compared to NAC and other prior cysteine prodrugs.